An aircraft gas turbine engine requires an automatic mechanism to shut it down should any of the rotor shafts break, which can result in a turbine over-speed condition and possible disc burst. In an aircraft engine, failure of the low-pressure turbine shaft (which is relatively less stiff and strong than the high-speed rotor shaft) for example, and the resultant uncontrolled speed increase of the driving side (the low pressure turbine) of the low-pressure turbine shaft, can lead to destruction of the engine and damage to the aircraft, thereby resulting a considerable danger to persons and property. Emergency engine shutdown is required and is typically accomplished by shutting down the fuel supply to the fuel nozzles of the engine. In gas turbine engines various devices for the mechanical or electronic detection of shaft failure and for the subsequent interruption of the fuel supply to avoid or control a dangerous over-speed condition, are well known. Generally, the known electronic safety systems of gas turbine engines are disadvantageous in that the time delay until shut off of the fuel supply is relatively long. High costs are also incurred by the required cooling or heat shielding of the sensors and electrical connections situated in the hot zone of the rotor shafts. The known mechanical shut-off systems conventionally employ, for example, a reference shaft co-axially associated with a turbine shaft, and connected to the driven end thereof. In the event of shaft failure the resultant rotation of the turbine shaft relative to the reference shaft, is used to mechanically actuate the fuel valve. This type of mechanical system also requires a relatively long corresponding time delay and results in more difficulties in the design and assembly of the engine.
Accordingly, there is a need to provide an improved emergency fuel shut-off system for gas turbine engines in the event of a shaft failure.